The performance of token ring local networks is adversely affected by the latency or time delay introduced by each station in the network. Station latency is defined as the time delay introduced in passing ring data through a station. Most token ring protocol standards (IEEE 802.5, ANSI X3T9.5) require encoding of each packet before transmission onto the ring. The encoding and decoding operations add significantly to the station latency.
A number of papers and printed materials have been published on this subject. The applicant is aware of the following references which disclose information which is more or less pertinent to the invention that is later disclosed and claimed in this application:
1. M. Schwartz, Computer Communication Networks Design and Analysis, Prentice-Hall, 1977, p. 275.
2. 2. W. Bux, "Local Area Subnetworks: Performance Comparison", IEEE Trans. Commun., vol. COM-29, pp.1465-1473, October, 1981.
3. R. C. Dixon, "Lore of the Token Ring", IEEE Network, vol. 1, pp. 11-18, January, 1987.
4. IEEE Standard: 802.514 1985 Local Area Networks Token Ring Access Method, Publication Number SH09944, IEEE Computer Society Press, 1985.
5. V. Iyer, S. Joshi, "FDDI's 100 Mbps Protocol Improves on 802.5 Spec's 4 Mbps Limit", EDN, May 2, 1985, pp. 151-160.
6. TMS380 Adapter Chipset User's Guide, Texas Instruments Incorporated, 1985, p. A-25.
7. AMD Applications Engineering, Applications Seminar, Technology, Circuits, Solutions, Advanced Micro Devices Incorporated, 1986, pp. 127-129.
8. M. J. Ferguson, "Mean Waiting Time for a Token Ring with Station Dependent Overheads", in R. L. Pickholtz (ed.), Local Area and Multiple Access Networks, Computer Science Press, 1986, pp. 43-67.
9. H. Takagi, Analysis of Polling Systems, MIT Press, 1986, p. 162.
10. David Everitt, "Simple Approximations for Token Rings", IEEE Trans. Commun., vol. COM-34, pp. 719-721, July, 1986.
The applicant is also aware of U.S. Pat. No. Re. 31,852, which is a reissue of U.S. Pat. No. 4,293,948, Olof Soderblom, which appears to be the pioneer patent in the field of token ring networks. This patent is directed to the basic operation of a closed loop data transmission system. The novelty in this invention appears to reside in the arrangement of the network into a loop, the procedure for the exchange of information among stations or terminal units on the network (by the use of framing bits), and by selectively actuating a switching unit which connects or disconnects the station from the network.
No reference or claim is made in Soderblom regarding the use of stations with two latency states to improve the performance of token ring networks.
Another patent of possible relevance is U.S. Pat. No. 4,195,351, Barner et al. The abstract of this patent refers to a data transmission system which includes stations connected in a closed loop configuration with interface capabilities at each station to connect to an external data processor. The network then allows simultaneous transmission of data among processors connected to stations on the loop. No mention is made of the use of stations with two latency states to improve the performance of token ring networks.
The effect of station latency on performance of token ring local networks has been recognized for some time. Schwartz (1 above) recognized the influence of walk-time on the performance of polling systems. Bux (2 above) analyzed the effect of station latency on message transfer delay of token rings and demonstrated the marked increase in delay produced by an increase in latency. More recently, recognition has been given to the effect of protocol design and of detailed station adapter implementation on the transmission delay performance of practical token ring networks. For example, Dixon (3 above) refers to the design of token ring protocols to eliminate practically all logical delay in the attached stations, and describes a principal design objective of token ring protocols as being the minimization of message transmission delays.